Internal thread rolling mandrel



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April 30, 1963 E. P. SUNDHOLM 3,087,174

INTERNAL THREAD ROLLING MANDREL Filed Feb. 11. 1960 VIIIIIIAIIIIIIIIIII' a 47 2 {NVEA/TOR' ATTORNEYS.

United States Patent Oflice 3,087,174 Patented Apr. 30, 1963 3,087,174 INTERNAL THREAD ROLLING MANDREL Edwin P. Sundholm, Albert City, Iowa Filed Feb. 11, 1960, Ser. No. 8,039 4 Claims. (Cl. 10-152) This invention relates to an internal thread rolling mandrel, or more specifically, to a thread rolling mandrel assembly for forming internally threaded caps.

The conventional means of forming threads on the inside of a tubular member is by a thread cutting tool which removes metal as the threads are formed. Attempts have been made to provide tubular members with internal threads by rolling the tubular member against and around a thread-forming mandrel. With tubular members which have a closed end, such as caps, it has been found to be very diflicult to remove them from the threading mandrel after the threads have been formed. Because of the relatively narrow width of the cylindrical wall of most caps, it is desirable to position the cap in relation to the threads on the mandrel by having the closed end of the cap engage the free end of the mandrel. Since the thread forming rollers which press the side wall of the cap into the threading portion of the mandrel will normally rotate around the mandrel in a direction tending to tighten the cap on the mandrel as the threads are formed, the closed end of the cap will be wedged very tightly against the free end of the mandrel on the completion of the threading operation. Consequently, the cap cannot be readily removed from the mandrel, and this makes the use of internal thread rolling procedures much less attractive for the production of caps than such procedures would otherwise be.

It is therefore an object of the present invention to provide an internal thread rolling mandrel, or mandrel assembly, which provides a solution to the problem described above. More specifically, it is an object of the present invention to provide a mandrel assembly which permits the cap to be positioned by clamping its closed end against the free end of the mandrel during the threading operation while at the same time permitting the cap to be readily unscrewed from the mandrel after the completion of the threading operation. Further objects and advantages will be indicated in the following detailed specification.

This invention is shown in an illustrative embodiment in the accompanying drawing, in which- FIGURE 1 is a side elevational view, partly in section, of a thread rolling machine with which the mandrel assembly of the present invention can be employed in the production of internally threaded caps;

FIGURE 2 is an enlarged fragmentary sectional view showing the mandrel of FIG. 1 and certain related parts, the mandrel and associated parts being shown as they would appear during the threading operation;

FIGURE 3 is a view similar to FIG. 2 except that the mandrel and associated parts are shown as they would appear after the completion of the threading operation and just prior to the removal of the completed cap;

FIGURE 4 is a side sectional view of a cap prior to threading; and

FIGURE 5 is a view similar to FIG. 4 showing the cap as it would appear after being threaded.

Looking first at FIG. 1, there is shown a thread rolling machine which includes a mandrel assembly M and a roller assembly R. This machine is adapted for use in forming threads on the inside of a cap, such as the cap C shown in FIG. 4, which has a cylindrical side wall a and a closed end b. In FIG. 1 the cap is also indicated by the letter C and is shown as it would appear on the completion of the threading operation. FIG. 5 illustrates the completed cap in section, which shows the internal threads I that have been formed by the threading operation. As explained in my copending application Serial No. 8,038, filed February 11, 1960, entitled Method of Forming Internally Threaded, Gasket-Retaining Caps, completed caps like the one shown in FIG. 5 of this application are particularly adapted for use as the dispensing head caps of cartridge-loading grease guns.

In the illustration given, the mandrel assembly M includes a support which is built-up from a base plate 10 and an upwardly extending post 11 which has its lower end bolted to base plate 10, as indicated in FIG. 1. A mandrel 12 is mounted on the support, and more specifically on the post 11. In the illustration given, the mandrel 12 extends into post 11 and is threadedly connected thereto. The arrangement is such that mandrel 12 remains in fixed relation to post 11 and base plate 10, although the whole assembly may rotate with base plate 10 where the base plate comprises part of a turntable providing a series of operating stations, one of which is the thread forming station shown in FIG. 1.

As indicated in FIG. 1, and shown more clearly in FIGS. 2 and 3, the mandrel 12 projects outwardly from the supporting post 11 and provides a free end portion adapted for insertion in the open end of the cap to be threaded, such as cap C of FIG. 4. As shown in FIGS. 2 and 3, this free end portion of mandrel 12 provides a cylindrical band of threads 13 adjacent the outer end of the mandrel for forming corresponding threads inside the cylindrical side wall a of the cap C.

In accordance with the present invention, a movable shoe 14 extends outwardly beyond the outer end of mandrel 12, as indicated in FIG. 1 and shown more clearly in FIG. 2. The outer end of shoe 14 should be adapted to firmly engage the inside surface of the closed end of the cap as the cap is being threaded. For example, in the illustration given, cap C provides a closed end with a substantially flat inside surface disposed at right angles to the axis of the cap. Similarly, the outer end of shoe 14 is made substantially fiat and is disposed at right angles to the axis of the mandrel 12. This permits the outer end of the shoe 14 to seat firmly against the inside of the cap end in the manner best illustrated in FIG. 2.

FIG. 2 is illustrative of the desired position of shoe 14 during the threading operation. It will be noted that in this position shoe 14 holds the closed end of cap C away from the outer end of mandrel 12. This clearance is indicated at 15 in FIG. 2.

To fully accomplish the objects of the present invention, the shoe 14 should be retractable to a position closer to the outer end of mandrel 12 than the position it occupies during the threading operation. In the illustration given, shoe 14 is retractable to the position illustrated in FIG. 3 where its outer end is in line with the outer end of mandrel 12. When the shoe 14 is thus withdrawn, it is disengaged from the cap end. The space between the cap end b and the shoe 14 is indicated at 16 in FIG. 3. By disengaging the shoe from the cap end the cap can be readily unscrewed from the mandrel after it has been threaded.

The mandrel assembly of this invention also includes means within the mandrel 12 for movably supporting the shoe 14, and also means for extending and retracting the shoe. In the illustration given, the mandrel 12 is provided with a longitudinal bore 17 which extends inwardly from the outer end of the mandrel. If desired, the outer end of bore 17 may be enlarged as indicated at 18 to provide a recess for receiving shoe 14 when it is fully retracted.

A pin 19 is slidably mounted within bore 17 with its outer end adjacent the free end of the mandrel 12. With this arrangement, shoe 14 can be supported by attaching it to the outer end of pin 19. In the illustration given, shoe 14 is formed integrally with pin 19. Also, the inward face 20 of shoe 14, as indicated more clearly in FIG. 2, has a conical shape which mates with the conical shape of recess 18. When the shoe 14 is fully retracted, as shown in FIG. 3, the conical surfaces 18 and 20 engage, and this provides a positive stop for the inward movement of shoe 14. To provide for the actuation of shoe 14, pin 19 extends through a bore in post 11 and into a block 21 which forms a lateral extension of post 11 and is releasably connected to post 11 by means of a lock nut 22, as indicated in FIG. 1. Pin 19 is prevented from rotating without interfering with the required degree of sliding movement by means of a key 23 which engages a slot 24.

Block 21 also provides a bore 25 which intersects the bore receiving pin 19 and is arranged at an angle thereto. In the illustration given, the axis of bore 25 forms a 90 angle with the axis of pin 19. The inner end of pin 19 extends into bore 25, and is provided with an inclined face 26 which is designed to function as a camming surface. A rod 27 is slidably received within bore 25, and is provided with an inclined camming face 28 which engages the face 26 of rod 19. The arrangement is such that when rod 27 moves upwardly, as indicated in FIG. 2, pin 19 moves in the direction of the free end of mandrel 12, and thus extends shoe 14. An adjustable stop is provided to limit the upward movement of pin 27, which in the illustration given comprises setscrew 29.

An air cylinder 30 is mounted on base 10, as shown in FIG. 1. A downward extension of block 21 connects with the upper end of air cylinder 30, and rod 27 extends within the cylinder where it is connected to a movable piston 31. A compressed air inlet 32 is provided beneath piston 31 so that when compressed air is applied to cylinder 30 piston 31 will move upwardly carrying rod 27 with it until the upper end of the rod strikes setscrew 29, or until shoe 14 has clampingly engaged the closed end b of the cap C. Normally, screw 29 will be positioned so that its lower end will just engage the top of rod 27 when shoe 14 is in its extended, or cap engaging position, as indicated most clearly in FIG. 2.

With the arrangement just described, as long as piston 31 is held in its elevated position by the air pressure within cylinder 30, shoe 14 will hold cap C away from the outer end of mandrel 12. As soon as the pressure is released within cylinder 30, however, piston 31 will drop down bringing rod 27 with it, and releasing the force applied to pin 19. This action causes shoe 14 to release its engagement with cap C, this position of the movable elements being shown in FIG. 3. It should be kept in mind that only a very small movement of the shoe 14 is required to accomplish the desired results. For example, a movement of ten to twenty thousandths of an inch will usually be sufiicient.

Preferably there is also provided a holding piece 33 supported within roller assembly R, as indicated in FIG. 1, and having an outer end adapted to engage the outer surface of the closed end of cap C. The desired relationship of these parts while the threads are being formed is shown in FIG. 2. It will be noted that the end b of the cap C is securely clamped between holding piece 33 and shoe 14, and that the holding piece and shoe are dimensioned to engage a major portion of the diameter of said cap. If desired, holding piece 33 can be backed by a spring.

Holding piece 33, while desirable, is not absolutely essential. The upward movement of rod 27 and thereby the outward movement of pin 19 and shoe 14 can be limited by means of setscrew 29. Shoe 14 will then engage the inside of cap end b but will not be clamped thereagainst. During the thread forming operation, however, the cap C will tend to tighten itself on the mandrel 12 and will thus press against the shoe 14 which is holding 1t away from the outer end of the mandrel. This arrangement thereby provides an alternate means for holding the outer end of the shoe 14 in engagement with the inside surface of the closed end of the cap as the cap is being threaded.

As indicated in FIG. 1, the roller assembly R includes a plurality of rollers 34 which are arranged circumferentially around the projecting end portion of mandrel 12, the rollers being carried between an assembly 35 and a guide plate 36. Assembly 35 includes a hydraulic-mechanical mechanism for moving the rollers inwardly until they engage the portion of the cap wall a opposite the threaded band 13 of the mandrel. In other words, assembly 35 and the rollers 34 rotate around the mandrel 12 on an axis of rotation corresponding with the axis of the mandrel. The individual rollers 34 are also free to rotate on their own axes. The relative position of the rollers 34 and the cap C during the thread rolling operation is indicated in FIG. 2. It will be noted that the rollers 34 press a portion of the cap wall inwardly against the threaded band 13, thereby forming corresponding threads on the inside of the cap. After the completion of the threading operation, the rollers 34 move outwardly to disengage the cap, and the cap is also disengaged from the holding piece 33 after the pressure has been released within cylinder 30 to permit shoe 14 to retract slightly. For example, after the clamping engagement of the shoe 14 has been released, plate 10 can be rotated carrying the mandrel and cap with it and thereby separating the cap from the holding piece 33. This position is indicated in FIG. 3. The cap can now be readily removed from the mandrel by unscrewing it manually or by a simple mechanical device. The completed cap after removal from the mandrel is shown in FIG. 5.

Where a holding piece 33 is employed as described above, and the holding piece is supported within the rotor assembly R, the holding piece should be rotatably mounted so that it can remain stationary while the assembly R rotates about the mandrel 12. In other words, during the thread rolling operation where the cap is clamped between the end of the holding piece 33 and the outer end of shoe 14, holding piece 33 will remain stationary except when the cap C rotates on the mandrel. Some rotation of the cap during the threading operation can be expected.

The rollers 34 will normally rotate around mandrel 12 and cap C in a direction tending to tighten the cap on the mandrel during the threading operation. This action is much as if the cap was already provided with threads and was being run onto the mandrel. The preferred direction of rotation, of course, will depend on whether the threads are left-handed or right-handed. When righthanded threads are being applied to the cap, the rollers will rotate clockwise when viewed in the direction of the free end of the mandrel.

While in the foregoing specification this invention has been described in relation to a specific embodiment thereof and many details have been set forth for purpose of illustration, it will be apparent to those skilled in the art that the invention is susceptible to other embodiments and that many of the details described herein can be omitted or varied without departing from the basic principles of the invention.

I claim:

1. A mandrel and roller assembly for use in forming threads on the inside of a metal cap having a cylindrical side wall and one closed end, comprising a support, a mandrel fixedly mounted on said support, said mandrel projecting outwardly from said support and providing a free end portion adapted for insertion in the open end of the cap to be threaded, said free end portion providing a cylindrical band of threads adjacent the outer end of said mandrel for forming corresponding threads inside the side wall of said cap, a roller assembly providing a plurality of rollers arranged circumferentially around the free end portion of said mandrel for rolling said cap side wall into the threads on said mandrel, a movable shoe extending outwardly beyond the outer end of said mandrel, means for holding the outer end of said shoe in engagement with the inside surface of the closed end of the cap as said cap is being threaded, said holding means including means for rotating said roller assembly relative to said cap in such a direction as to tighten said cap on said mandrel while said cap is being threaded, thereby holding said closed end away from the outer end of said mandrel as said cap is being threaded, means for retracting said shoe to a position closer to the outer end of said mandrel for disengaging said shoe from said cap end, whereby said cap can be readily unscrewed from said mandrel after it has been threaded, and means within said mandrel for movably supporting said shoe.

2. The mandrel and roller assembly of claim 1 wherein said mandrel has a longitudinal bore extending inwardly from its outer end, and said means for movably supporting said shoe comprises a pin slidably mounted in said bore with its outer end adjacent the free end of said mandrel, said shoe being connected to the outer end of said pin and carried thereby.

3. The mandrel and roller assembly of claim 1 wherein said means for holding said shoe in engagement with said cap comprises a compressed air cylinder providing a movable piston, and a force transferring linkage extending from said piston to said shoe, said linkage being arranged so that when air pressure is applied to said cylinder, said shoe is forced outwardly to a position in engagement with the cap on said mandrel.

4. A mandrel and roller assembly for use in forming threads on the inside of a metal cap having a cylindrical side wall and one closed end, comprising a support, a mandrel fixedly mounted on said support, said mandrel projecting outwardly from said support and providing a free end portion adapted for insertion in the open end of the cap to be threaded, said free end portion providing a cylindrical band of threads adjacent the outer end of said mandrel for forming corresponding threads inside the cylindrical side wall of said cap, a roller assembly providing a plurality of rollers arranged circumferentially around the free end portion of said mandrel for rolling said cap side wall into the threads on said mandrel, a movable shoe extending outwardly beyond the outer end of said mandrel, means for holding the outer end of said shoe in engagement with the inside surface of the closed end of the cap as said cap is being threaded, thereby holding said closed end away from the outer end of said mandrel as said cap is being threaded, said means including a holding piece providing a face adapted to engage the outside surface of the closed end of said cap as said cap is being threaded, thereby permitting said cap to be clamped between said shoe and said holding piece as said cap is being threaded, said shoe and said holding piece being dimensioned to engage a major portion of the diameter of said cap, means for retracting said shoe to a position closer to the outer end of said mandrel for disengaging said shoe from said cap end and releasing the clamping engagement between said cap and said holding piece, whereby said cap can be readily unscrewed from said mandrel after it has been threaded, and means within said mandrel for removably supporting said shoe.

References Cited in the file of this patent UNITED STATES PATENTS 1,546,091 Lewis July 14, 1925 2,353,253 Liverrnont July 11, 1944 2,400,024 Roehrl May 7, 1946 2,647,553 Sharf Aug. 4, 1953 2,799,049 Wilson July 16, 1957 

1. A MANDREL AND ROLLER ASSEMBLY FOR USE IN FORMING THREADS ON THE INSIDE OF A METAL CAP HAVING A CYLINDRICAL SIDE WALL AND ONE CLOSED END, COMPRISING A SUPPORT, A MANDREL FIXEDLY MOUNTED ON SAID SUPPORT, SAID MANDREL PROJECTING OUTWARDLY FROM SAID SUPPORT AND PROVIDING A FREE END PORTION ADAPTED FOR INSERTION IN THE OPEN END OF THE CAP TO BE THREADED, SAID FREE END PORTION PROVIDING A CYLINDRICAL BAND OF THREADS ADJACENT THE OUTER END OF SAID MANDREL FOR FORMING CORRESPONDING THREADS INSIDE THE SIDE WALL OF SAID CAP, A ROLLER ASSEMBLY PROVIDING A PLURALITY OF ROLLERS ARRANGED CIRCUMFERENTIALLY AROUND THE FREE END PORTION OF SAID MANDREL FOR ROLLING SAID CAP SIDE WALL INTO THE THREADS ON SAID MANDREL, A MOVABLE SHOE EXTENDING OUTWARDLY BEYOND THE OUTER END OF SAID MANDREL, MEANS FOR HOLDING THE OUTER END OF SAID SHOE IN ENGAGEMENT WITH THE INSIDE SURFACE OF THE CLOSED END OF THE CAP AS SAID CAP IS BEING THREADED, SAID HOLDING MEANS INCLUDING MEANS FOR ROTATING SAID ROLLER ASSEMBLY RELATIVE TO SAID CAP IN SUCH A DIRECTION AS TO TIGHTEN SAID CAP ON SAID MANDREL WHILE SAID CAP IS BEING THREADED, THEREBY HOLDING SAID CLOSED END AWAY FROM THE OUTER END OF SAID MANDREL AS SAID CAP IS BEING THREADED, MEANS FOR RETRACTING SAID SHOE TO A POSITION CLOSER TO THE OUTER END OF SAID MANDREL FOR DISENGAGING SAID SHOE FROM SAID CAP END, WHEREBY SAID CAP CAN BE READILY UNSCREWED FROM SAID MANDREL AFTER IT HAS BEEN THREADED, AND MEANS WITHIN SAID MANDREL FOR MOVABLY SUPPORTING SAID SHOE. 